Why metric ?what is the need? when a router learns about one network through multiple sources then router has to choose when one should be updated in the topology table and based upon this it updates routing table..to do this all it depends on metrics to the destination network learned by different sources.so, what is the metric formula? it is like ..
metric = [(K1*Bandwidth + K2*Bandwidth/{256-Load} + K3*Delay) *K5/(K4+Reliability)]*256
but by default EIGRP doesn't use all the K-values ,it uses only K1 and K3,
K1=1
K2=0
K3=1
K4=0
K5=0
so if we keep the K-values as above in the metric formula then it becomes.
metric=256*[10^7/bandwidth + Delay ]
bandwidth=lowest bandwidth (kbps) in the path
Delay =cumulative delay(micro sec)/10
i am going to explain this theory with an example but before i 'd like to show how to configure these K-values to calculate the metric of our own without depending on the EIGRP default values.
LONDON(config)#router eigrp 90
LONDON(config-router)#me
LONDON(config-router)#metric ?
holddown Enable EIGRP holddown
maximum-hops Advertise EIGRP routes greater than <hops> as unreachable
weights Modify EIGRP metric coefficients
LONDON(config-router)#metric we
LONDON(config-router)#metric weights ?
<0-8> Type Of Service (Only TOS 0 supported)
LONDON(config-router)#metric weights 0 ?
<0-255> K1
LONDON(config-router)#metric weights 0 1 1 1 1 1
LONDON(config-router)#
*Mar 1 01:42:00.467: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.0.1 (Serial0/0) is down: metric changed
*Mar 1 01:45:39.231: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.1.2 (FastEthernet1/0) is down: K-value mismatch
As you can see step-by-step, changing k values leads to mismatch with one of the neighbor ,here is the key point ,to become neighbors metric should be same on both the routers otherwise the routers tear off their neighbor-ship.
consider the following setup which has three routers ,here metric is calculated by router in the form of FD and RD.
FD=feasible distance
RD=reporting distance
i mentioned the bandwidth and delay on the two links,consider that EIGRP is configured and there is full adjacency ,now here i show the topology table of R1 router
R1 has two entries for 10.0.0.0/30 network and 192.168.1.0/30 network,R1 calculated FD for its local network and remote network 192.168.1.0/30, how does this FD is calculated by R1?
metric=FD= 256*[10^7/256 + 20000/10] = 10511872 this is FD for 10.0.0.0/30 network
metric=FD= 256*[10^7/128 + 40000/10] = 21024000 this is FD for 192.168.1.0/30 network
if we observe the FD calculation of 192.168.1.0/30 network by R1 the bandwidth is considered as 128kbps which is lowest bandwidth and cumulative delay 20000+20000 of both links
and if you see the RD of 192.168.1.0/30 network is 20512000 which R2 is calculated for its local network and telling to R1 as reporting distance RD
i hope u understand the concept of metric ,FD and RD
please post your comments..
metric = [(K1*Bandwidth + K2*Bandwidth/{256-Load} + K3*Delay) *K5/(K4+Reliability)]*256
but by default EIGRP doesn't use all the K-values ,it uses only K1 and K3,
K1=1
K2=0
K3=1
K4=0
K5=0
so if we keep the K-values as above in the metric formula then it becomes.
metric=256*[10^7/bandwidth + Delay ]
bandwidth=lowest bandwidth (kbps) in the path
Delay =cumulative delay(micro sec)/10
i am going to explain this theory with an example but before i 'd like to show how to configure these K-values to calculate the metric of our own without depending on the EIGRP default values.
LONDON(config)#router eigrp 90
LONDON(config-router)#me
LONDON(config-router)#metric ?
holddown Enable EIGRP holddown
maximum-hops Advertise EIGRP routes greater than <hops> as unreachable
weights Modify EIGRP metric coefficients
LONDON(config-router)#metric we
LONDON(config-router)#metric weights ?
<0-8> Type Of Service (Only TOS 0 supported)
LONDON(config-router)#metric weights 0 ?
<0-255> K1
LONDON(config-router)#metric weights 0 1 1 1 1 1
LONDON(config-router)#
*Mar 1 01:42:00.467: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.0.1 (Serial0/0) is down: metric changed
*Mar 1 01:45:39.231: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 90: Neighbor 10.0.1.2 (FastEthernet1/0) is down: K-value mismatch
As you can see step-by-step, changing k values leads to mismatch with one of the neighbor ,here is the key point ,to become neighbors metric should be same on both the routers otherwise the routers tear off their neighbor-ship.
consider the following setup which has three routers ,here metric is calculated by router in the form of FD and RD.
FD=feasible distance
RD=reporting distance
i mentioned the bandwidth and delay on the two links,consider that EIGRP is configured and there is full adjacency ,now here i show the topology table of R1 router
R1 has two entries for 10.0.0.0/30 network and 192.168.1.0/30 network,R1 calculated FD for its local network and remote network 192.168.1.0/30, how does this FD is calculated by R1?
metric=FD= 256*[10^7/256 + 20000/10] = 10511872 this is FD for 10.0.0.0/30 network
metric=FD= 256*[10^7/128 + 40000/10] = 21024000 this is FD for 192.168.1.0/30 network
if we observe the FD calculation of 192.168.1.0/30 network by R1 the bandwidth is considered as 128kbps which is lowest bandwidth and cumulative delay 20000+20000 of both links
and if you see the RD of 192.168.1.0/30 network is 20512000 which R2 is calculated for its local network and telling to R1 as reporting distance RD
i hope u understand the concept of metric ,FD and RD
please post your comments..
